The invention relates generally to punch set assemblies used in punch presses, and particularly to adjustable length punch set assemblies wherein the punch may be adjusted to compensate for punch blade length reduction due to sharpening.
Repeated use of a punch assembly in a punch press operation results in the natural dulling and wear of the punch blade or tip. Once the tip has become dull, the effectiveness of the punch assembly is reduced and the punch tip must be sharpened. Sharpening may be accomplished by grinding the end of the punch tip, and this results in shortening the length of the blade and, consequently, the punch. The length of the punch then must be adjusted to compensate for the ground-off portion of the punch blade.
A first type of punch set assemblies that allow for length corrections are exemplified in U.S. Pat. Nos. 4,031,787 and 4,141,264. These patents disclose punch sets that compensate for the shortened punch blade length by adding shims, washers or other similar objects to the punch. The problem with this method is that the added washers or the like are usually weak and cannot withstand the constant cyclical forces placed upon a punch. Also, the length of the punch tip can only be adjusted within certain limits before it becomes too short for effective operation, thereby limiting the number of times the punch tip can be sharpened. In addition, most such methods that allow for the adjustment of the length of the punch tip require dismantling of the entire punch in order to access the punch tip for adjustment; this obviously can be a rather time-consuming process. Additionally, once the punch has been reassembled, further effort is frequently expended in determining how much the sharpening and adjusting steps have affected the axial position of the tip with reference to the plane of the stripper plate opening that it extends through in use.
Improvements on these known methods are described in commonly assigned U.S. Pat. No. 4,375,774 and in U.S. Pat. No. 5,131,303. In these patents, the punch driver and punch holder or body components of the punch are attached by mutually engageable threaded portions so that overall punch length adjustment may be accomplished by rotation of the threaded portions. Locking mechanisms are provided in each case. In the ""774 patent, an expandable locking pin is inserted into aligned locking pin holes wherein it interferes with and prevents rotation of the threaded portions. While simplifying the axial length adjustment process, this approach requires removal and re-insertion of the locking pin.
In the ""303 patent, the assembled punch is axially slidably received within a bore provided in a punch guide. A releasable lock for locking the threaded ends against relative rotation is provided by an arcuate wire clip having a radially inwardly extending cam pin. The arcuate clip is retained in an annular groove and radially inwardly extending bore in the punch holder so that the cam pin extends inwardly and into engagement with a set of circumferentially distributed grooves in the male threaded end of the punch body. Length adjustment in either direction is provided by rotating the punch body with respect to the punch holder so that the cam tip is released from one groove and engages a further groove.
An adjustable length forming tool head is disclosed in U.S. Pat. No. 5,020,407 which discloses a length adjustment in the threaded connection between the punch driver and the punch head base which in turn is attached to a form tool body. A length control ring member is spring biased away from and between the driver and the base and is formed with a central opening for engaging the shaft of the driver to prevent their relative rotation and a set of circumferentially spaced apertures for engaging a pair of pins extending from the base. Adjustment is accomplished by grasping the ring member and driver to withdraw the ring member from engagement with the pins and to rotate them until the next desired set of diametrically opposed apertures is aligned with the pins. Since the form tool does not have a punch set spring encircling the punch head, it is possible to grasp the ring member and make the length adjustment. Such an arrangement would not be useable in punch sets having a punch spring encircling the punch head, driver and holder components of the type disclosed in the above referenced patents and application.
Another adjustable length punch tool is disclosed in commonly assigned U.S. Pat. No. 5,329,835. The tool includes a punch holder secured to a punch with a mounting bolt. The punch holder is threadably engaged with the punch driver. The length of the punch tool is adjusted by rotating the punch driver relative to the punch holder about the engaged threads. The punch driver would be free to undesirably rotate about the punch holder, but for the inclusion of a locking button.
The ""835 patent locking button has a generally square, cubic shape having upper square corners and a square profile. The button is biased upward by a biasing spring to force the square button top into a downwardly open, square receiving pocket in the punch driver. The square lower body of the button is slidably received within an upwardly open square pocket in the punch holder. In the upwardly biased, locked position, the square button acts as a key, preventing rotation between the punch driver and the punch holder by extending between the two. When the button is depressed further into the receiving pocket in the punch holder, for example by an operator depressing the accessible button, the bottom no longer bridges the punch driver and punch key, and the punch driver may be rotated relative to the punch holder. The button is thus in contact with the punch driver, and may occasionally, after frequent repeated blows by the ram, become worn by interaction between button and punch driver upper receiving pocket. This is undesirable.
What would be desirable is a punch tool having a punch driver rotation lock that is less likely to become worn through the repeated pounding action of the ram. What would also be advantageous is a locking mechanism allowing access from outside the punch tool, not requiring operator access through the top central bore of the punch tool.
The present invention provides a punch tool which can be used with punch presses. The punch tool includes generally a punch driver and a punch element. The punch element can include a punch secured to a punch holder together with a punch guide, with the punch holder and punch slidably received within the punch guide. The punch driver, during production use, can be forced by a hydraulic ram downward, forcing the attached punch holder and punch axially downward, past the bottom of the punch guide, and through a work piece against a receiving die. The effective length of the punch tool can be adjusted, as the punch holder and punch driver can be threadably mated together. The threaded punch driver can be rotated relative to the punch holder, punch, and punch guide, thereby lengthening or shortening the effective length of the punch tool. The punch tool may need to be periodically adjusted to compensate for the shortening of the punch lower portion caused by wear and by grinding to sharpen the punch cutting surface.
As free and uncontrolled rotation of the punch driver relative to the punch holder is undesirable, the present invention provides mechanisms for enabling and disabling rotation of the punch driver relative to the punch holder, punch, and punch guide. The present invention provides a locking disk or collar secured to the punch driver as well as a latch secured to the punch guide. In a locked position, the latch prevents rotation of the locking disk relative to the latch, thereby preventing rotation of the attached punch driver relative to the punch holder. In an unlocked position, the latch permits rotation of the locking disk and attached punch driver relative to the punch holder.
With respect to axial movement, the punch driver, locking disk, punch holder, and punch move together as one when forced by a ram. With respect to rotation, rotation of any of the punch driver, locking disk, punch holder, punch, and punch guide are typically prevented during production. When adjustment of the effective length of the punch tool is desired, the punch driver and locking disk rotate together relative to the punch holder, punch, punch guide, and latching member which typically move together as one, and which do not rotate. Unlocking the latch, therefore, allows the punch driver and locking disk to be rotated relative to the other parts.
In one punch tool, the tool includes a punch element with a punch having a lower punch tip or cutting tip, and a punch driver element having an upper surface adapted to be engaged by the ram of a punch press in a punching operation. The punch element and punch driver element can be axially aligned and threaded together to enable axial adjustment of the length of the combined punch driver and punch in response to relative rotation of the punch driver and punch. One of the punch driver element or punch element can have a latch adjacent its periphery, spaced apart from its axis, and moveable along an axis parallel to the axis of the punch element and punch driver element. The latch can be moveable between an upper, locked position, preventing relative rotation of the elements, and a lower unlocked position, permitting relative rotation of the elements. The latch can include a spring having a predetermined spring constant acting to urge the latch into its upper locked position, the latch having a sufficiently low mass and the spring having a sufficiently great spring constant so as to prevent the latch from unintentional movement into the unlocked position in response to a striking of the punch driver element by a punch press ram during a punching operation.
In another punch tool, the punch element includes a punch guide having a bore, through which the punch axially moves in a punching operation, and the punch guide includes an upper peripheral portion having a housing receiving the latch and spring. The punch driver element can include a plurality of axially extending cavities receptive of the latch when the latch is in its upper locked position, to prevent rotation of the punch driver element with respect to the punch guide.
In still another punch tool, the punch guide has an upper rim and the punch driver includes a locking disk positioned beneath the upper rim of the punch guide. The disk can have a plurality of circumferentially spaced grooves in its outer periphery defining the cavities in position to receive the latch when the latch is in its upper, locked position. In another embodiment, the punch tool includes a latch having a body configured to be actually received in the grooves of a locking disk, the latch body having a recess along its length that receives the disk when the latch is moved to its lower unlocked position to enable the disk to rotate with respect to the latch. In yet another embodiment, the latch includes a manually accessible surface extending upwardly no higher than the rim to facilitate manual downward movement of the latch. In still another embodiment, the punch guide has a generally cylindrical outer surface, and carries the housing at least partially outside of the cylindrical surface to facilitate manual operation of the latch.
Yet another punch tool includes a punch driver element having an outer periphery with vertically extending, circumferentially spaced, downwardly open slots defining the cavities in position to receive the latch when the latch is in its upper, locked position. In one tool punch embodiment, the latch includes a vertically extending shaft slidable vertically in the housing, and a manually accessible outwardly protruding key mounted to the shaft to facilitate manual movement of the shaft.